1. Field of the Invention
The present invention relates to integrated circuit packaging technology, and more particularly to wafer-level ball grid array packages.
2. Background Art
Integrated circuit (IC) chips or dies are typically interfaced with other circuits using a package that can be attached to a printed circuit board (PCB). One such type of IC die package is a ball grid array (BGA) package. BGA packages provide for smaller footprints than many other package solutions available today. A BGA package has an array of solder ball pads located on a bottom external surface of a package substrate. Solder balls are attached to the solder ball pads. The solder balls are reflowed to attach the package to the PCB.
An advanced type of BGA package is a wafer-level BGA package. Wafer-level BGA packages have several names in industry, including wafer level chip scale packages (WLCSP), among others. In a wafer-level BGA package, the solder balls are mounted directly to the IC chip when the IC chip has not yet been singulated from its fabrication wafer. Wafer-level BGA packages can therefore be made very small, with high pin out, relative to other IC package types including traditional BGA packages.
A current move to tighter fabrication tolerances, such as 65 nm, with a continuing need to meet strict customer reliability requirements and ongoing cost pressures, is causing difficulties in implementing wafer-level BGA package technology. During operating conditions or reliability assessment testing, external stresses are applied to the wafer-level BGA package. These stresses are transferred to the package through a solder interconnect. For wafer-level packaging, two polymer layers in the package are typically required to act as a stress buffer between the solder interconnect and the die. However, having two polymer layers present in a BGA package is expensive.
Thus, what is needed are improved wafer-level packaging fabrication techniques that can meet desired reliability requirements and ongoing cost pressures, while enabling even tighter fabrication tolerances and smaller packages sizes.